Contactless ignition system for internal combustion engine

ABSTRACT

A contactless ignition system is provided with an ignition charge discharge condenser for charging an induced voltage of a generating coil, a first switching element, triggered to conduct when an induced voltage of a generating coil reaches a predetermined level, for supplying a charged voltage into an ignition coil, and a trigger control condenser for charging induced voltages of the generating coil and the trigger coil, and triggering of the first switching element caused by an induced voltage of the generating coil is inhibited by a second switching element during a specified discharge time following charging of the trigger control condenser.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a contactless (non-contact) ignitionsystem for an internal combustion engine for automatically subjectingignition timing to spark advance control and spark retardation controlfrom a low rotational speed range to a high rotational speed range.

2. Related Art

As a contactless ignition system for an internal combustion engine ofthe related art, for example, at the time of rotation of a rotor havingmagnetic poles, a generating coil charges an induced voltage into anignition charge and discharge condenser, and electrical charge chargedinto the ignition charge and discharge condenser is supplied to anignition coil through switching elements that are switched by a voltageinduced by a trigger coil.

In this type of contactless ignition system, if the rotational speed ofthe internal combustion engine, namely the rotational speed of therotor, is increased, then together with that increase in speed thecharge discharge timing of the ignition charge discharge condenser isadvanced, and finally the rotational speed of the internal combustionengine is increased in excess of a set rotational speed and sometimesresults in damage to the engine.

Devices adopting a governor mechanism and devices utilizing electroniccontrol have therefore been proposed as devices for preventing overspeedof an internal combustion engine.

However, the governor mechanism requires a large operating space becauseof expansion and contraction effects while rotating integrally with acrank shaft, and there is the drawback that lifespan is shortened due tomechanical operation.

Also, with an engine overspeed prevention device that uses electroniccontrol, there is a problem that because complicated electroniccircuitry is used it is not possible to realize cost reduction.

SUMMARY OF THE INVENTION

The present invention has been conceived in view of the above describedsituation, and an object of the invention is to provide a compact andinexpensive contactless ignition system for an internal combustionengine that can improve starting performance and horsepower whilecausing advancement of ignition timing from low engine speed to normalengine speed, and that can prevent engine overspeed by causingretardation of ignition timing at above normal engine speed.

In order to achieve this object, a contactless ignition system for aninternal combustion engine of the present invention comprises a rotorhaving magnetic poles arranged either side of a magnet, a core with twolegs, arranged opposite the rotor, wound with a trigger coil on the oneleg and with a generating coil on the other leg positioned opposite tothe rotational direction of the rotor with respect to the one leg, anignition charge discharge condenser for charging an induced voltage ofthe generating coil, a first switching element, triggered to beconductive when an induced voltage of the generating coil has reached apredetermined (specified) trigger level, for supplying a voltage chargedin the ignition charge discharge condenser to an ignition coil, atrigger control condenser for charging induced voltages of thegenerating coil and the trigger coil, and a second switching element forinhibiting a trigger of the first switching element caused by inducedvoltage of the generating coil for a specified time following charge ofthe trigger control condenser.

In the present invention, at the time of startup, since ignition timingof the internal combustion engine is advanced, kick back (a phenomenonwhere a piston is pushed back immediately after ignition and thecrankshaft rotates backwards due to piston speed being slow whenstarting) does not occur, and stable startup and increased speed can beexpected. Also, in a normal engine speed range, it is possible tosufficiently maintain horsepower of the engine by sufficiently advancingthe ignition timing. On the other hand, in a high engine speed region inexcess of the normal engine speed, since the ignition timing can beretarded there is the advantage that it is possible to prevent engineoverspeed.

As a preferred embodiment, it is possible for the second switchingelement to be a transistor that short-circuits the two ends of thetrigger coil within a specified time of discharge of the trigger controlcondenser, to inhibit triggering of the first switching element. In thisway, triggering of the first switching element can be implemented usinga low cost circuit structure.

As another preferred embodiment, it is possible for the trigger controlcondenser to comprise a time constant circuit for determining adischarge time constant of the trigger control condenser in order toachieve ignition timing retardation control. In this way, there is theadvantage that it is possible to select rotational speed of the enginethat causes the ignition timing retardation to start easily and withhigh precision by setting the discharge time constant of the timeconstant circuit.

As another preferred embodiment, it is possible to provide a circuitprotection trigger circuit to trigger the first switching element in ahigh voltage below capacity voltage of the ignition charge dischargecondenser. In this embodiment, charge volume does not go beyond capacityvoltage of the ignition charge discharge condenser. Therefore, it ispossible to prevent damages of each section of the circuit including theignition charge discharge condenser.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram showing a contactless ignition system for aninternal combustion system of an embodiment of the present invention.

FIG. 2 is a front elevation showing a partial cross section of theessential structure of the contactless ignition system of FIG. 1.

FIG. 3 is a timing chart showing voltage waveforms for each section ofthe circuit shown in FIG. 1 in a normal rotational engine speed range.

FIG. 4 is a timing chart showing voltage waveforms for each section ofthe circuit shown in FIG. 1 in a high rotational engine speed range.

FIG. 5 is a timing chart showing voltage waveforms for each section ofthe circuit shown in FIG. 1 in an engine overspeed range.

PREFERRED EMBODIMENT OF THE INVENTION

In FIG. 2, a rotor 3 constituting a contactless (non-contact) ignitionsystem for an internal combustion engine of this embodiment has a pairof magnetic poles 6 and 7 either side of a magnet 5 embedded in anon-magnetic body 4 such as a body of aluminum, for example. Part ofeach of the magnetic poles 6 and 7 are exposed at an outer surface ofthe rotor 3, and can be made opposite to end surfaces of two legs 8 a, 8b of a core 8 during rotation of the rotor 3.

The core 8 is an angular U shaped-member facing the rotor 3, and agenerating coil 1 and a trigger coil 2 are respectively wound around thelegs 8 a and 8 b. The trigger coil 2 is wound around the one leg 8 b,and the generating coil 1 is wound around the other leg 8 a positionedopposite to the rotational direction of the rotor 3 with respect to theone leg 8 b. Surfaces of the legs 8 a and 8 b opposite to the rotor 3are formed in an arc shape so as to maintain a constant distance fromthe rotor 3.

In FIG. 1, a diode 9, an ignition charge discharge condenser 10 and aprimary coil 11 a of an ignition coil 11 are connected in series withthe generating coil 1, thus constituting a charging circuit for charginga positive voltage induced by the generating coil 1.

The ignition charge discharge condenser 10 is connected in series withthe anode and cathode of a thyristor 12, as a first switching element, adiode 15 and the primary coil 11 a of the ignition coil 11, and thisseries connection constitutes a discharge circuit for dischargingcharged up charge of the ignition charge discharge condenser 10. Thisdischarge circuit functions to discharge charge charged into theignition charge discharge condenser 10 to the ignition coil 11 when thethyristor 12 is triggered and made to conduct.

A spark plug 13 is connected to the secondary coil 11 b of the ignitioncoil 11, and an LC oscillation diode 14 for the primary side of theignition coil 11 is connected between the anode and cathode of thethyristor 12.

A resistor 16 connects the gate of the thyristor 12 to the point ofconnection between the cathode of the thyristor 12 and the diode 15. Aseries circuit comprising a resistor 17 and a diode 18 is connected inparallel to the diode 15 through the resistor 16.

On the other hand, a resistor 19, a diode 20, a trigger controlcondenser 21 and the diode 15 are connected in series to the two ends ofthe trigger coil 2. Also, a resistor 22 and a diode 23 are connected inseries between a circuit linking the generating coil 1 with the diode 9and a circuit linking the diode 20 with the trigger control condenser21.

Resistors 24 and 25 constituting a time constant circuit together withthe trigger control condenser 21 are connected in series to the two endsof the trigger control condenser 21, and the base of a transistor 26, asa second switching element, is connected to the point of connectionbetween these two resistors 24 and 25. The collector of the transistor26 is connected to a circuit linking one end of the trigger coil 2 andthe diode 15. Also, the emitter of the transistor 26 is connected to acircuit linking the generating coil 1 and the diode 9 through a resistor27 and a diode 28. The collector of the transistor 26 is also connectedto the gate of the thyristor 12 through the diode 18 and the resistor17. A reverse current prevention diode 29 is connected to the two endsof the trigger coil 2. Also, a circuit protection trigger circuit 31having a resistor 30 is connected between the circuit linking thegenerating coil 1 with the diode 9 and the gate of the thyristor 12. Thecircuit protection trigger circuit 31 triggers the thyristor 12 in ahigh voltage below capacity voltage of the ignition charge dischargecondenser 10.

Next, operation of the contactless ignition system for an internalcombustion engine having the above-described structure will bedescribed. First of all, if the engine is activated and the rotor 3rotates in the direction of arrow A in FIG. 2, voltages having thewaveforms shown in FIG. 3(a) and FIG. 3(b) are respectively induced inthe generating coil 1 and the trigger coil 2 on the core 8 opposite therotor 3. The induced voltage of the trigger coil 2 is generated laterthan the induced voltage of the generating coil 1. Of induced voltage inthe generating coil 1, a positive voltage is applied to the primary coil11 a of the ignition coil 11 through the diode 9 and the ignition chargedischarge condenser 10 and electric charge is charged into the ignitioncharge discharge condenser 10.

On the other hand, of voltage induced in the trigger coil 2, positivevoltage rises later than the positive induced voltage of the generatingcoil 1, by a predetermined period, and this voltage charges the triggercontrol condenser 21 through the resistor 19 and the diode 20, 15. Thetrigger control condenser 21 is also charged by the positive inducedvoltage from the generating coil 1, to give a charge voltage waveform asshown in FIG. 3(c). After charging of the ignition charge dischargecondenser 10, if the gate voltage of the thyristor 12 reaches aspecified level, namely if the induced voltage of the trigger coils 2reaches an initial trigger level LL shown in FIG. 3(a), the thyristor 12is turned on and electric charge of the ignition charge dischargecondenser 10 is supplied though the thyristor 12 to the ignition coil11. As a result, an ignition voltage is applied from the ignition coil11 to the spark plug 13, and a fuel air mixture inside the fuel chamberof the internal combustion engine is ignited. By repeating thisoperation, the engine is started and then increased in speed, andhorsepower, being the engine output, is increased by advancing theignition timing.

Then, in a process for changing induced voltage of the trigger coil 2from positive to negative, charge having the charge voltage waveformshown in FIG. 3(c) that has been charged into the trigger controlcondenser 21 is discharged through the resistors 24 and 25 and thetransistor 26 is turned on. As a result, the series circuit of thetransistor 26, the resistor 27 and the diode 28 shunts the generatingcoil 1, and during this time triggering of the thyristor 12 is inhibitedso the thyristor 12 is OFF.

Accordingly, when the engine speed becomes high beyond a normal speedrange, the generating cycle of the induced voltage of the generatingcoil 1 becomes short. The width of the induced voltage on the time axisbecomes wide, and, as shown in FIG. 4, the thyristor 12 is triggeredlate for a retardation width T1. Thereby, the discharge of the chargevoltage R of the ignition charge discharge condenser 10 begins to beretarded. Specifically, as shown in FIG. 4, if the engine speed exceedsa normal engine speed corresponding to a set time constant of the timeconstant circuit, the ignition timing is gradually retarded, and as aresult it is possible to prevent overspeed of the engine.

After starting the engine, from a low speed range to a specified normalspeed range, reaching the normal speed NR, the ignition timing is notaffected by the time constant and is advanced rapidly together withincrease in engine speed. Accordingly, together with carrying out stablestartup of the engine, it is possible to prevent the occurrence of kickback (a phenomenon where a piston is pushed back immediately afterignition and the crankshaft rotates in reverse due to slow piston speedat the time of startup) caused by delay on cranking, and since ignitiontiming is advanced as much as possible in the normal engine speed rangeit is possible to sufficiently maintain engine horsepower. Also, byusing the trigger coil 2, it is possible to simplify the circuitstructure for ignition timing control.

On the other hand, if the engine speed becomes higher beyond the highspeed range, the generating cycle of induced voltage of the generatingcoil 1 becomes shorter as shown in FIG. 5, and triggering of thethyristor 12 is inhibited when the transistor 26 turns on by thedischarge voltage of the trigger control condenser 21. Thereby,supplying the ignition coil 11 with ignition current is prevented, andit is possible to prevent overspeed of the engine. At the same time, thecharge voltage gradually rises in the ignition charge dischargecondenser 10. When the charge voltage reaches a specified level HL belowcapacity voltage of the ignition charge discharge condenser 10, triggercurrent flows at the gate of the thyristor 12 through the resistor 30.Thereby, the thyristor 12 turns on and electrical charge of the ignitioncharge discharge condenser 10 is discharged into the ignition coil 11,which makes perfect the protection of the ignition charge dischargecondenser 10 and other sections in the circuit.

What is claimed is:
 1. A contactless ignition system for an internalcombustion engine, comprising, a rotor having magnetic poles arrangedeither side of a magnet, a core with two legs, arranged opposite therotor, wound with a trigger coil on the one leg and with a generatingcoil on the other leg positioned opposite to the rotational direction ofthe rotor with respect to the one leg, an ignition charge dischargecondenser for charging an induced voltage of the generating coil, afirst switching element, triggered to be conductive when an inducedvoltage of the generating coil has reached a predetermined triggerlevel, for supplying a voltage charged in the ignition charge dischargecondenser to an ignition coil, a trigger control condenser for charginginduced voltages of the charging coil and the trigger coil, and a secondswitching element for inhibiting a trigger of the first switchingelement caused by induced voltage of the generating coil for a specifiedtime following charge of the trigger control condenser.
 2. Thecontactless ignition system for an internal combustion engine accordingto claim 1, wherein the second switching element is a transistor forshort-circuiting both ends of the trigger coil for a specified chargingtime of the trigger control condenser to prevent triggering of the firstswitching element.
 3. The contactless ignition system for an internalcombustion engine according to claim 1, wherein the trigger controlcondenser constitutes a time constant circuit for determining adischarge time constant of the trigger control condenser in order toperform ignition timing retardation control.
 4. The contactless ignitionsystem for an internal combustion engine according to claim 1, furthercomprising a circuit protection trigger circuit to trigger the firstswitching element in a high voltage below capacity voltage of theignition charge discharge condenser.